Thanks for the link to a working I2C Sniffer. I have added it to this (basic) page: https://github.com/Testato/SoftwareWire/wiki/I2C-Sniffers.
It is possible to translate that code and then find the things that you want:
S0100000W = Start, Address 0x20, Write command
00001000 = Data byte 0x08
s = Stop
Can you tell more about your project ?
Do you want that information in a Arduino ? Could you add code to the Master Arduino ?
Do you want to analyze that information on a computer ? Then you better buy a 30 dollar LHT00SU1.
Do you only need to read pin P3 ? Can you connect P3 to a digital input pin of a Arduino board ?
There is an option to put an Arduino board between the Master and the Slave. Using the hardware I2C bus on one side and a software I2C bus on the other side. Since it can not directly respond to a request of the Master (that information has to be requested from the Slave), the project must allow that and the sketch might have to poll the Slave all the time to update the status.